The physical properties of commercially available CPVC pipe are widely extolled and deservedly so. These properties include (a) a high distortion temperature under load (DTUL), also referred to as heat distortion (or deflection) temperature (HDT); (b) ductility at a relatively low temperature; and, (c) a high resistance to rupture (high hoop strength) even when carrying water at 82.2° C. (180° F.) under 690 KPa (100 psig, pounds per square inch gauge) pressure. Combined with the excellent corrosion resistance of CPVC, such properties decreed that the pipe could be used in hot and cold water and other aqueous distribution systems in both industrial and domestic installations where continuous service under these conditions was demanded. By “continuos service” is meant that the pipe is subjected to the aforesaid conditions without interruption over a period of 50 years.
To meet this requirement for continuous service, the CPVC pipe having a most preferred concentration of Cl in the range from 65 wt. % to 69 wt. %, is disclosed in U.S. Pat. No. 5,591,497 (the '497 patent) to Hartitz. The formulated compound is blended with post-chlorinated polyethylene (CPE), an impact modifier, stabilizer, plasticizer, glass transition temperature (Tg) enhancing additive, lubricant, pigment, and the like. As stated in the '497 patent, the amount of “high rubber” impact modifier “comprising a polydiene and one or more hardening monomers” used in the CPVC compound (the mixture to be extruded) has an effect on (i) melt flow rate which affects control of the extrudate, inter alia; (ii) heat distortion temperature; (iii) tensile modulus; (iv) dynamic thermal stability; and (v) weathering. (see col. 1, lines 40-43). A “high rubber” impact modifier is one which contains more than 50 wt. % of a pre-formed rubbery polydiene substrate such as a 1,3-diene polymer or copolymer thereof, in particular of butadiene and/or isoprene, referred to herein as a “polydiene”.
The chemical structure and amount of “flow enhancers” used in the CPVC compound has an effect on (i) tensile modulus; (ii) brittleness at low temperature; (iii) tensile strength; and (iv) heat distortion temperature (see col. 1, lines 44-47). In particular, lubricants, both internal (within the extrudate) and external (between the extrudate and the walls of the extrusion die), processing aids and plasticizers, if used, and CPE used in a CPVC compound, each contributes its effect towards flow. The precise function of the CPE is not known, but it is believed to function as a flow enhancer, whether plasticizer, processing aid or lubricant.
The '497 patent provides illustrative examples showing how choice of ingredients in the CPVC compound affects physical properties of pipe made from 68.5% Cl CPVC. But, the patent contains no suggestion that, either the concentration of Cl in the CPVC and the molecular weight (measured as inherent viscosity “I.V.”) of the precursor PVC, the concentration of CPE, or the choice of both the type and amount of particular ingredients in a formulated CPVC compound will affect the physical properties of the CPVC pipe extruded. In particular, there is no suggestion that either the Cl concentration of the CPVC and I.V. of the precursor PVC, the concentration of CPE, or the type of impact modifier, inert filler, lubricant and stabilizer, and the amount in which each is used, would make a disproportionately large difference in the physical properties of the pipe, especially as measured by the notched Izod impact strength and hydrostatic design basis “HDB”. HDB is the estimated tensile strength in the wall of the pipe in the circumferential orientation that when applied continuously will cause the pipe to rupture or burst at 100,000 hrs. (see ASTM D2837-01). By “inert” is meant that the filler does not react with any of the ingredients of the CPVC compound.
To improve the long term performance and reliability, thus providing a higher degree of safety over continuous use, it was decided to try and modify the formulation of the CPVC compound disclosed in illustrative example 7 of the '497 patent, which example meets the requirements of cell class 2-4-4-4-7, that the new formulation may meet the more stringent requirements of a higher cell class, namely 2-4-4-4-8. The first numeral “2” in the cell class designation specifies CPVC pipe; the second numeral (whether “3” or “4”) specifies the level of notched Izod impact strength—“3” indicates at least 80.1 J/m (1.5 ft.lb/in) of notch, “4” indicates at least 266.9 J/m (5 ft.lb/in) of notch; the third numeral “4” specifies tensile strength of at least 48.3 MPa (7,000 psi); the fourth numeral “4” specifies tensile modulus of at least 2482 MPa (360,000 psi); and the fifth numeral (whether “7” or “8”) specifies the level of DTUL or HDT measured under 1.82 MPa (264 psi) load. Numeral “7” indicates DTUL or HDT of at least 100° C., and “8” indicates DTUL, or HDT of at least 110° C. (see ASTM D1784).
The '497 patent specifies the high rubber impact modifier as being an “ABS graft copolymer (which) has a Shore D hardness generally less than about 64 and preferably in a range between about 35 and 45, and non-ABS graft copolymer having a Shore D hardness between 35 and less than 42” (see col. 4, lines 2-5) indicating that there is nothing critical about either the type of graft, or the hardness of the high rubber impact modifier chosen. The acronym “ABS” refers to styrene and acrylonitrile grafted on a polydiene-containing backbone.
Illustrative examples 1, 2, 6 & 7 of the '497 patent do not identify the impact modifier used beyond stating that it is an “ABS graft copolymer with a Shore D hardness of 44” (Exs. 1, 2 and 7), or “with a Shore D hardness of 64” (Ex. 6). Example 5 substitutes 7 parts of a Shore D 42 MBS graft copolymer for the ABS impact modifier. The acronym “MBS” refers to methylmethacrylate and styrene grafted on a polybutadiene or styrene-butadiene backbone. Without knowing which of the many commercially available “high rubber” ABS or MBS graft copolymer impact modifiers was used, it is not possible to determine its hardness. Examples 3 and 4 use no impact modifier.
The '497 patent teaches using CPVC with Cl content “preferably between about 65 wt. % and 69 wt. %” but cautions that “where the chlorine content is outside of the specified range, CPVC exhibits characteristics which render it unsuitable in the present invention. Above the maximum specified chlorine level, the compositions derived therefrom would exhibit inadequate processing properties, poor impact properties and inadequate dynamic thermal stability for the intended use”. (see col. 4, lines 18-24).
Though the illustrative examples used CPVC with a 68.5 wt. % Cl content, and the most preferred molecular weight range of the precursor PVC was quantified by an inherent viscosity from 0.7 to 1.2, the effect of either the Cl content of the CPVC, or the I.V. of the precursor PVC, on the physical properties of the impact modified CPVC, was not recognized. The 68.5 wt. % Cl content was consistent with the requirement that CPVC pipe for hot and cold water use should be “high Cl” content pipe, to provide a desirable high HDT, the choice of the particular concentration being in the range from 67 wt. %-70 wt. % Cl. Whatever I.V. in the broad range it happened to be, was only coincidental. In particular, there is no suggestion that Cl content would have an effect on either the notched Izod impact strength or the HDB (see ASTM D2837-01); and no suggestion that choice of I.V. in a particular narrow range of at least 0.88, preferably from 0.88-1.05, combined with particular choices of filler and its particle size, the concentration of CPE having specified Cl content, and a high rubber impact modifier, would have a very large effect on either the notched Izod impact strength or the HDB, or both.
Referring to a “high-strength blend of CPVC and styrene-acrylonitrile (SAN) copolymer having a chlorine content between 60.5 wt. % and 64.5 wt. %”, disclosed in U.S. Pat. No. 4,647,646, the '497 patent states: “The blend exhibits improved tensile strength, however a particularly high tensile strength in the absence of improved impact resistance and in particular, an absence of low temperature ductility is not useful for hot and cold water distribution system (HCWD) components such as plumbing pipes and fittings or in drain-waste-vent systems. A combination of properties is required. Upon impact modification of this blend, a loss in HDT and modulus is predicted”. (see '497, col. 2, lines 33-42). The observation that “impact modification” of the “low Cl” compound was predicted to result in a loss of HDT and modulus, does not indicate whether the amount of modifier used was either increased or decreased. Nor is there any indication how the Cl content of the CPVC, particularly if it was above 67 wt. %, might affect the properties imparted by the modifier, if at all, irrespective of its chemical structure or the amount used. Indicating that the tensile strength was improved in CPVC with a Cl content lower than 64.5 wt. % does not suggest the HDB would also be increased, as the HDB is a measure of the strength of the pipe, not its tensile strength.
The CPVC pipe currently sold meets the cell classification requirements of ASTM D2846 as outlined in ASTM D1784, as it must, by choosing the appropriate mixture of ingredients in the CPVC compound. The difficulty of doing so, despite knowing that the properties of the extrudate will be affected by both the chemical structure and the amount of each key ingredient (identified in the '497 patent as being the flow enhancer, and, the impact modifier), is set forth in six of the seven illustrative examples of the '497 patent.
In each of the examples of the '497 patent, long term hydrostatic stress rupture (LTHS) testing was conducted for only between about 190 hr and 600 hr at 82.2° C. (180° F.), but there is no indication under what specific pressures the test was conducted (see col. 9, lines 55-59). Yet, the extrapolation is stated “to predict the 100,000 hour intercept value”. The requirement for arriving at a predicted HDB is specified in ASTM D2837-01; the minimum testing time for each of several samples is 10,000 hr under sequential pressures at 82.2° C. (180° F.). In view of this strict requirement, it is not reasonable to accept the prediction made from the tests of record. The longest test was run only 6% of the test period specified by the ASTM test (test run for between 190 hr and 600 hr instead of 10,000 hr). The 100,000 hr intercepts predicted in each of the examples of the '497 patent are based on data over too short a period of time to be credible though measured values on impact strength would be.
Reference herebelow is to each of seven examples in the '497 patent, in each of which the CPVC compound was formulated with 100 parts by weight of CPVC with a Cl content of 68.5 wt. %, the stated amount of CPE having a Cl content in the range from 30%-40% but of unspecified molecular weight (see '497 col. 1, lines 53-54), 5 parts of titanium dioxide (“pigment”) of unspecified particle size, and specified amounts of lubricant, stabilizer and an inadequately identified impact modifier.
The disclosure relating to the titanium dioxide used, is silent as to its particle size and no hint of its critical effect on impact strength and HDB. There is no mention of the use of an antioxidant which is found useful to maintain the desired physical properties at the extrusion temperature of “high Cl” CPVC pipe in the range from 200° C.-225° C.
Referring to the 100,000 hr intercept, the '497 states: “A ¾ inch (19 mm) standard dimension ratio 11 (SDR-11), copper tube size (cts) (copper tubing specifications), pipe extruded directly from a powder composition exhibited an unexpected ductility during low temperature drop impact testing and exceeded the minimum long term hydrostatic stress rupture requirement of ASTM D2846”. (see col. 3, lines 55-60).
“SDR” refers to “standard dimensions ratio” defined as: [Do/t] where “Do” is the average outside diameter, and “t” is the minimum wall thickness.
The pressure rating is determined by the formula:
      2    ×    HDB    ⁢                  ⁢    Rating    ⁢                  ⁢    of    ⁢                  ⁢    the    ⁢                  ⁢    Material    ×          (              safety        ⁢                                  ⁢        factor            )            SDR    -    1  
For an SDR-11 pipe made with CPVC requiring that it have HDB of 1000 psi, and for which the safety factor is 0.5, the pressure rating is:100 psig=(1000 psi)/(11−1).If the same SDR-11 pipe is tested with a material that has a HDB of 1250 psi (8.62 MPa), the pressure rating is: (1250 psi)/(11-1)=125 psig, that is, 25% higher than with a material that has a HDB of 1000 psi. The safety factor, also known as service design factor, is specified in TR-9/2002 of the Plastic Pipe Institute (PPI). The safety factor for CPVC water pipes is specified as 0.5 by PPI for calculating pressure rating of the pipe. Thus, the safety factor used in this specification and claims is 0.5 in all examples. Should the safety factor be changed in the future by the applicable standards organization, then the pressure rating of the pipe would change according to the formula above.
The credibility of using measurements which were made between about 190 hr and 600 hr at 82.2° C. (180° F.), coupled with there being no indication under what specific sequential pressures the tests were conducted (see col. 9, lines 55-59), were evidently not an issue in the '497 patent since the aim in the illustrative examples appears to have been not to meet or exceed the minimum HDB requirement of 1000 psi (6.89 MPa) at a 100,000 hr intercept, as specified by ASTM D2846, but only to obtain an approximate indication of the long term hydrostatic stress rupture (LTHS).
In each of the following examples from the '497 patent, the compound consisting essentially of 100 parts 68.5 wt. % Cl and blended ingredients was both, formed into plaques for testing, and conventionally extruded into 19 mm (¾″) SDR-11 pipe. The I.V. of the precursor PVC from which the 68.5 wt. % CPVC was made is 0.90.
In Example 1 of the '497 patent, the CPVC was extruded with 9 parts of an impact modifier, namely an “ABS graft copolymer having a Shore D hardness of 44”, presumably a graft copolymer of styrene and acrylonitrile on polybutadiene, (see col. 6, lines 28-30), 2.2 parts lubricant (polyethylene “PE” and polyethylene oxide “PEO”, see col. 7, lines 39-40), and 5 parts of titanium dioxide (referred to as pigment, see col. 7, lines 60-61), is used. There is no indication of the particle size of the titanium dioxide. This combination of lubricant and titanium dioxide is used in all the examples. The compound resulted in a plaque which had a notched Izod impact strength of 9.5 ft.lb/in of notch (507.1 J/m of notch), the tensile modulus was 342,200 psig (2,359 MPa) and the tensile strength was 7,745 psi (53.39 MPa). The pipe indicated a predicted 100,000 hr intercept of 1,242 psi (8.562 MPa). Though the impact strength and 100,000 hr intercept appear to be excellent, the pipe fails to meet the minimum tensile modulus required by ASTM D-2846.
Note that, since measurements in the '497 patent were made over a period of between about 190 hr and 600 hr at 82.2° C. (180° F.) (see col. 9, lines 55-59) neither this Example 1, nor any of the other examples refers to the 100,000 hr intercept predicting a HDB value as specified in ASTM D2837-01.
In Example 2 of the '497 patent, the CPVC was extruded with 7 parts of the same impact modifier as that used in Example 1. The decrease of 2 parts of modifier resulted in a tensile strength of 8,088 psi (5.575 MPa); a tensile modulus of 390,800 psi (2,694 MPa); the drop impact strength of 34.9 ft.lb (47.3 N-m) does not state how it was measured. The compound exhibited poor processing characteristics and was deemed unsuitable for extrusion. The predicted 100,000 hr intercept was 1,365 psi (9.410 MPa).
In Example 3 of the '497 patent, the CPVC was extruded with 9 parts of CPE and no impact modifier, other ingredients being the same. The result was a plaque with tensile strength of 7,956 psi (54.84 MPa), a tensile modulus of 346,000 psi (2,385 MPa) which was an increase relative to Example 1, and an Izod impact of 1.9 ft.lb/in (101.4 J/m) which was lower than in Examples 1 and 2. The drop impact strength was 21.1 ft.lb. (28.6 N-m), but how it was measured is not stated. The predicted 100,000 hr intercept of only 161 psi (1.09 MPa), indicates that the concentration of CPE has a large effect on the burst strength of the pipe.
In Example 4 of the '497 patent, the CPVC was extruded with 2 parts of CPE and no impact modifier, other ingredients being the same. The result was a plaque with tensile strength of 8678 psi (59.82 MPa), and a tensile modulus of 393,000 psi (2,709 MPa). The notched Izod impact strength was 0.7 ft.lb/in of notch (37.36 J/m of notch). The drop impact value was 5 ft.lb. (6.7 N-m) (how tested, or the ASTM test used, is not stated); the ductility at 40° F. (4.4° C.) was 12 ft.lb. (16.25 N-m). The compound failed ductility tests required. The pipe fails to meet the requirements of ASTM D2846. The 100,000 hr. intercept was 535 psi (3.688 MPa).
In Example 5 of the '497 patent, the CPVC was extruded with 2 parts of CPE and 7 parts of methacrylate butadiene styrene (MBS) impact modifier, Shore D 42, other ingredients being the same. MBS resins are defined as “graft copolymers of methylmethacrylate and styrene grafted on polybutadiene or styrene-butadiene rubbers” ('497, col. 6, lines 34-36). The result was a plaque with HDT of 99° C.; tensile strength of 8,089 psi (55.76 MPa); a tensile modulus of 360,600 psi (2,485 MPa); and a notched Izod impact strength of 7.7 ft.lb/in of notch (411 J/m of notch). The 100,000 hr. intercept for the pipe was 1,170 psi (8.06 MPa) (meets ASTM D2846 requirement) but the pipe did not meet the minimum HDT requirement. This particular MBS (non-ABS) impact modifier at 7 parts in combination with CPE at 2 parts is stated to have failed to meet the HDT requirement. It has now been found that such MBS graft copolymer impact modifiers, in the novel preferred CPVC compound, readily meet the HDT requirement specified in the '497 patent.
In Example 6 of the '497 patent, the CPVC was extruded with 2 parts of CPE and 7 parts of an ABS impact modifier, Shore D 64, other ingredients being the same. Varying the chemical structure and hardness of the impact modifier relative to Example 5 gave plaques with HDT of 100° C.; tensile strength of 8,352 psi (57.57 MPa); a tensile modulus of 450,300 psi (3,104 MPa); and a notched Izod impact strength of 2.0 ft.lb/in of notch (106.7 J/m of notch). The 100,000 hr. intercept for the pipe was 1,306 psi (9.003 MPa) (meets ASTM D2846 requirement) but its cold temperature ductility was unsatisfactory.
Example 7 of the '497 patent provides the best mode of the pipe extruded from a compound including the 100 parts CPVC, 2 parts CPE, and 7 parts impact modifier, namely an “ABS graft copolymer having a Shore D hardness of 44”, presumably a graft copolymer of styrene and acrylonitrile on polybutadiene, (see Example 1), other ingredients being the same. The plaques had a HDT of 101° C.; a tensile strength of 7,997 psi (55.13 MPa); a tensile modulus of 363,500 psi (2,505 MPa); and a notched Izod impact strength of 7.7 ft.lb/in of notch (411 J/m of notch). The 100,000 hr. intercept for the pipe was 1,242 psi (8.562 MPa) (exceeds ASTM D2846 requirement); its ductility was satisfactory and met requirements of ASTM D-1784. Note, though, its HDT of 101° C. meets the requirements of cell class 2-4-4-4-7, it does not meet the HDT requirement of cell class 2-4-4-4-8.
Since this Example 7 of the '497 patent presented the best mode, it was decided to repeat the example, as best as the description in the example allows, with a test extending over at least 10,000 hr before obtaining the 100,000 hr intercept. The inventors having now found that the most effective impact modifiers are those specified herein, one of the most effective, namely Blendex® 338 (an ABS graft copolymer) was used to duplicate Example 7 of the '497 patent.
To improve the pipe so that it does meet the HDB requirement of “at least 1250 psi at 100,000 hr” as well as the requirement of cell class 2-4-4-4-8, the concentration of CPE in the CPVC compound was left at 2 parts because this was the concentration used in Example 7, and because it functions mainly as a flow enhancer which at higher concentrations than 3 parts has an adverse effect on burst strength. Based on experimental observation that the effect of one specific commercially available, grafted, “high rubber” ABS graft copolymer impact modifier was not greatly different from another of the same genus having a different graft, it was decided, in the tests run, to choose one, namely the Blendex® 338, and vary only the amount used. Accordingly, Blendex® 338 was used at 6 parts, in combination with 2 parts CPE. The impact modifier has a Shore D hardness of 44, measured at 22° C. (ASTM D2240).
At present, BlazeMaster® CPVC SDR-13.5 pipe in iron pipe size (IPS) is formulated with 4 parts of Blendex® 338 impact modifier per 100 parts of “high Cl content” CPVC in a compound formulated for use in extruded pipe sold for sprinkler systems, to control fire in office and residential buildings, warehouses and other enclosed spaces. This pipe for sprinkler systems was configured as SDR-13.5 to meet the dimension requirements of ASTM F-442 and the pressure requirements of UL-1821 which requires the pipe carry a maximum working pressure of 1.307 MPa (175 psi)@65.5° C. (150° F.). Because the high Cl content provides a desired high HDT which readily meets the requirements of ASTM F-442, and the relatively low temperature requirement is also readily satisfied, there was no concern of greater safety. When the BlazeMaster® pipe was tested under ASTM D2837-01, it met the requirement of an HDB of 1250 psi (8.62 MPa) at 100,000 hr; because pipe for sprinkler systems is not used for domestic and industrial hot and cold water, the BlazeMaster® pipe was not tested under ASTM D2846. However, BlazeMaster® pipe is made from a material that does not meet a cell class of at least 2-4-4-4-7.
The Problem:
Though CPVC pipe currently sold meets the cell classification requirements (2-3-4-4-7) of ASTM D2846, the pipe's HDB of 1000 psi (6.89 MPa) at 100,000 hr provides a less than optimal margin of safety for the performance of pipe required to meet a demand for continuous service under stated conditions of elevated pressure, 690 KPa (100 psig), and temperature, 82.2° C. (180° F.), over a period of 50 years. The safety and performance of the pipe are a function of its HDB and notched Izod impact strength. It was decided to try and provide, for users seeking a higher level of performance safety than required under ASTM D2846, CPVC pipe which ensures greater safety and reliability in continuous service than that provided with currently available CPVC pipe. Greater safety and reliability would be provided by pipe in a higher cell class than currently required; which pipe would meet the higher standard of 1250 psi (8.62 MPa) HDB specified in Table 1 of ASTM D2837, preferably, exceed it. More preferably, the pipe would meet the aforesaid higher standard and also have both, a notched Izod impact strength and an annealed HDT higher than provided by a randomly chosen high rubber graft copolymer impact modifier. Annealing a plaque is effected at 100° C. for 24 hr.
If the CPVC compound could be reformulated to provide pipe with a 25% higher pressure rating than required (HDB of 1250 psi vs. HDB 1000 psi), then SDR-11 pipe could provide the higher margin of safety. On the other hand, if the user was satisfied with the margin of safety afforded by the requirements of ASTM D2846, then the user could use SDR-13.5 pipe which, having a thinner wall thickness, would provide higher flow and lower pressure drop than SDR-11 pipe of the same diameter but thicker wall thickness. Also, the SDR-13.5 pipe would be lighter in weight and require less CPVC material to produce the pipe. The lighter weight would make the pipe easier to install and transport.
The Solution:
By dint of laborious trial and error, involving continuous experimentation over several years, the accumulated data from tests presented below indicated an unexpected effect resulting from the combination of what appeared to be only minor changes in the prior art formulation. In particular, it was found that high Cl content CPVC with Cl in the range from 66.5 to 70 wt. %, made from poly (vinyl chloride) polymer (PVC) with a minimum I.V. of 0.88, combined with from 5 phr (parts per 100 parts of CPVC polymer) to 6 phr of particular “high rubber” impact modifiers having specified structure; from 1.25-3 phr of stabilizer, preferably an organotin stabilizer, optionally a co-stabilizer can be used in conjunction with the stabilizer, co-stabilizers such as salts of carboxylic acids, disodium phosphate, sodium citrate, zeolite and hydrotalcite are suitable; from 1.5-3 phr of CPE; and 1-7 phr, preferably 3-5 phr of filler. The filler is preferably either carbon black or titanium dioxide filler having a primary particle diameter in the range from about 0.01 μm to less than 3 μm with about 90% of the particles being in the range from about 0.01 μm to less than 2 μm, preferably from 0.1-1 phr of an antioxidant is used, from 1.3-3.5 phr of a lubricant, and other conventionally used ingredients such as processing aids, and pigments being used in conventional ranges, provided a solution to the problem. Moreover, the effective impact modifier is a graft copolymer which requires that its rubber content be in the range from more than 50% by weight to less than 90% by weight, preferably 60-85% by weight, and when it is a graft copolymer, the graft content is the remainder.
Not only did the CPVC compound reformulated with the critical amount of graft copolymer of acrylonitrile-styrene on a polydiene rubber provide a plaque with a notched Izod impact strength of at least 5 ft.lb/in (266.9 J/m), instead of the required 1.5 ft.lb/in (80.1 J/m), but the plaque and pipe also met all other performance requirements for cell class 2-4-4-4-8 (instead of lower cell class 2-3-4-4-7). In particular, the pipe made from the CPVC compound met the requirement that it have a HDB of at least 1250 psi at the 100,000 hr intercept.
The extrusion compound specified herein is narrowly defined within critical limits, both by the concentration of Cl in the CPVC, and the amount of one or more specific impact modifiers used in combination with other ingredients. The concentration of CPE was kept the same as that in the best mode stated in Example 7 of the '497 patent. Since the concentration of each of the other ingredients is not disclosed in the '497 patent, they are used in the narrow ranges specified below to get the desired results.
The combination of ingredients including using a CPVC with high Cl content and less modifier unexpectedly results in extruded CPVC pipe which has at least a 25% higher HDB as measured according to the requirements of ASTM D2837 than required, and higher impact strength than that obtained with 7 parts by weight of impact modifier; and the novel pipe is qualified in cell class 2-4-4-4-8.